The refractive-index profile of optical fiber devices is of critical importance for determining the subsequent performance of optical fibers and fiber devices. For example, the refractive-index profile of dispersion-compensating optical fiber is tailored to achieve specific levels of dispersion at telecommunication wavelengths. As another example, polarization-maintaining optical fiber relies on circular asymmetry present in the fiber structure to decouple orthogonal polarization states. Moreover, small, irregular index variations can also impact optical fiber and fiber devices—this is especially true if such variations lead to asymmetry in the transverse refractive-index profile. Varied indices of refraction can also cause birefringence in optical fiber devices, which alters transmission spectra and introduces polarization dependent loss.
Most refractive-index profiling techniques are designed to measure optical fiber devices with azimuthally symmetric (axisymmetric) refractive-index profiles. This includes both higher resolution interferometric and non-interferometric techniques. Of the techniques capable of two-dimensional index profiling, they either lack sufficient index resolution for characterizing certain devices (such as quantitative phase imaging) or are destructive (such as etching-atomic force microscopy). Thus, an alternative system capable of high-resolution refractive-index profiling of azimuthally asymmetric optical fiber (devices) is desired.